This introduces `singularNameProvider`. This provider will be used
by core types to have their singular names are defined in discovery
endpoint. Thanks to that, core resources singular name always have
higher precedence than CRDs shortcuts or singular names.
This adds new integration tests to test shortnames and
singular names are expanding to correct resources.
In this case, core types have always higher precendence than
CRDs.
When CRDs are deleted, discovery local cache is not invalidated.
This brings about `resource not found` error when new CRD with same name is created
with different fields(ie. changing scope from cluster-wide to namespaced).
Because this already deleted CRD still stays in serverresources.json and kubectl tries to use it.
This local cached files have 10 minutes TTL. After deletion, if user waits 10 minutes,
files will be expired and deleted and there will be no errors. However, 10 minutes is a long time
and cache needs to be invalidated after deletion occurs.
This PR adds a document into delete command by noting that there might be a need to invalidate discovery
cache when CRD is deleted. In addition to that this PR adds a test to catch this behavior.
